iMac not loading past loading screen after power outage

No, there is no need for it in the Apple Store. If they install a new drive, then they usually format it and install OS X on it, but if you would prefer doing that yourself then ask them not to. I would, however, bring that Snow Leopard DVD that wouldn't load. You want to be sure that gets fixed.

Great. The disc won't actually eject now so it will definitely be there.

Thanks for your help. My one anxiety is that the time machine will work. My partner shares it and they used their Mac book air to try and see if they could see the contents of my drive. But it says no mountable file system when they click on my backup.

Five ways to eject a stuck CD or DVD from the optical drive

Ejecting the stuck disc can usually be done in one of the following ways:

1. Restart the computer and after the chime press and hold down the

left mouse button until the disc ejects.

2. Press the Eject button on your keyboard.

3. Click on the Eject button in the menubar.

4. Press COMMAND-E.

5. If none of the above work try this: Open the Terminal application in

your Utilities folder. At the prompt enter or paste the following:

/usr/bin/drutil eject

If this fails then try this:

Boot the computer into Single-user Mode. At the prompt enter the same command as used above. To restart the computer enter "reboot" at the prompt without quotes.

Have them try booting from your Time Machine backup per the instructions sent above. If they cannot open the disk at all, then it could be damaged. If that's the case, then you probably do want to take it with you to the Apple Store to see if they can fix it.

If you have an OS X installer disc in the optical drive and boot from it, then all you can do is use Disk Utility to repair or erase the drive and install a version of OS X from the disc. If you click on Recovery-10.8 then you are starting from the Mountain Lion Recovery HD partition installed when Mountain Lion was installed. You can repair the drive and/or erase it using Disk Utility. You can reinstall Mountain Lion over your existing Mountain Lion system if you do not erase the drive first. You want to do this provided you do not want to erase your data. You would do the following:

Reinstalling OS X Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears.

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the indented Macintosh HD entry from the the left side list. Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Continue button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless and more reliable.

It has been awhile. Refresh my memory. Your computer now starts normally when in Safe Mode, but does not load from a normal startup? Remind me what is now occurring when you try a normal startup?

This may be a problem with the login file(s). Which version of OS X is installed now? If it's Yosemite do you know if you let it enable FileVault by default? If so, then see: FileVault bug makes Yosemite pause or hang at login | MacIssues.

Another thought is that there is a damaged block on the drive where the login files are stored so that they are corrupted. Or, this may apply to cache files. Repairing the hard drive will not find bad blocks so even though they may exist, the drive will still pass repair. The only way to deal with bad blocks is to either replace the drive or see if you can Zero them out by using a one-pass Zero Data security option when erasing the drive.

Do not install Yosemite until this issue is resolved. I'd like you to see if the following applies in Mountain Lion.

Clearing Caches to Fix Login Problem

You will need to type some Unix commands. If you are not comfortable with this, I don't know of anything other than a re-install. But if you are careful, you should be OK. I recommend you print this out in a largish mono-spaced font so you don't miss any spaces (or add extra ones). Note that case is important.

Be careful. Some of these commands are dangerous, since you are going to be root.

Start up in Single-user Mode. When this has finished you will see a prompt ending in '#', although there may be other messages. Enter the following commands after the prompt:

/sbin/fsck -fy

Press RETURN. Wait a few seconds for 8-10 lines of output. If the last line says repairs were carried out, repeat this command until you get a message 'The volume <yourdiskname> appears to be OK'. Then continue with:

/sbin/mount -uw /

cd /Library/Preferences

rm com.apple.loginwindow.plist

rm com.apple.windowserver.plist

cd /Library/Caches

rm -r *

cd /System/Library

cd /System/Library/Caches

rm -r *

reboot

Press RETURN after each command.

This should now take you to a proper login screen after the normal boot sequence. You should then Repair Permissions by using Disk Utility (in your /Applications/Utilities folder).

Print out the commands to be sure you will enter them correctly. If a file cannot be found just move on to the next line. Please be careful as these commands execute automatically upon entry. Note spaces that exist in the lines.